title: Enzymatically active prostate-specific antigen promotes growth of human prostate cancers.
abstract: BACKGROUND
  Prostate specific antigen (PSA) is the best-known member of the kallikrein-related peptidase family, with an established role as a prostatic disease biomarker. Although it is produced at high levels by all stages of prostate cancer, it is uncertain if PSA plays a role in prostate cancer initiation and progression. We decided to investigate the impact of PSA and its enzymatic activity on tumor cell growth rates.
  
  
  METHODS
  A gene-specific shRNA lentiviral construct reduced endogenous PSA expression in the LNCaP human prostate cancer cell line. Resulting changes in growth rates in vitro and in vivo were determined. Using a mass spectroscopy-based approach, alterations to the LNCaP proteome due to reduced PSA were measured. Finally, to evaluate the importance of PSA's proteolytic activity, the PSA-null Du145 human prostate cancer cell line was engineered to express either enzymatically inactive pro-PSA (WT) or a furin-activated variant (FR) with high enzymatic activity. The resulting clones were evaluated for PSA-induced changes in growth rates in vivo and in vitro.
  
  
  RESULTS
  Lowered PSA levels dramatically reduced LNCaP growth rates. Expressing active PSA (FR), but not the inactive WT variant, conferred a growth advantage on Du145 cells. Proteomics analysis revealed global changes to the LNCaP proteome as a result of reduced PSA expression.
  
  
  CONCLUSIONS
  These studies demonstrate the importance of PSA to prostate cancer cell growth. We also show that the enzymatic activity of PSA confers an enhanced growth rate to human prostate cancer cells, suggesting a causal role in prostate cancer progression.
authors.affiliation: The Sidney Kimmel Comprehensive Cancer Center, The Johns Hopkins University School of Medicine, Baltimore, Maryland, USA. swilli87@jhmi.edu
authors.forename: Simon A
authors.initials: SA
authors.lastname: Williams
authors.forename: Christine A
authors.initials: CA
authors.lastname: Jelinek
authors.forename: Ivan
authors.initials: I
authors.lastname: Litvinov
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Cotter
authors.forename: John T
authors.initials: JT
authors.lastname: Isaacs
authors.forename: Samuel R
authors.initials: SR
authors.lastname: Denmeade
mesh_terms: D000818:Animals; D001681:Biological Assay; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000502:physiology; D003001:Cloning, Molecular; D006801:Humans; D007150:Immunohistochemistry; D008297:Male; D013058:Mass Spectrometry; D051379:Mice; D008819:Mice, Nude; D017430:Prostate-Specific Antigen / Q000235:genetics / Q000378:metabolism*; D011471:Prostatic Neoplasms / Q000201:enzymology* / Q000235:genetics / Q000473:pathology; D040901:Proteomics / Q000379:methods; D034741:RNA, Small Interfering / Q000494:pharmacology
chemical_list: D034741:RNA, Small Interfering; D017430:Prostate-Specific Antigen